The condition of believing in the present results in having eternal life.
John 10:28 - I give them eternal life, and they shall never perish; no one will snatch them out of my hand.
And in this verse, Jesus was clear: those given eternal life WILL NEVER PERISH.
How is that not eternal security for those given eternal life?
Please explain how the condition of believing is no longer required after a person has repented and believed.
Unbelief is plainly described as not continuing to believe, which is described as not continuing to obey.
Unbelief is Disobedience.
Unbelief is not continuing to believe.
If a person believes for a while, then no longer believes, they are no longer a believer, having returned to unbelief.
12 Beware, brethren, lest there be in any of you an evil heart of unbelief in departing from the living God; 13 but exhort one another daily, while it is called “Today,” lest any of you be hardened through the deceitfulness of sin. 14 For we have become partakers of Christ if we hold the beginning of our confidence steadfast to the end, 15 while it is said:
“Today, if you will hear His voice, Do not harden your hearts as in the rebellion.”
16 For who, having heard, rebelled? Indeed, was it not all who came out of Egypt, led by Moses? 17 Now with whom was He angry forty years? Was it not with those who sinned, whose corpses fell in the wilderness? 18 And to whom did He swear that they would not enter His rest, but to those who did not obey? 19 So we see that they could not enter in because of unbelief. Hebrews 3:12-19
Eternal life is promised to those who believe, not those who do not believe.
Same exact thing Jesus taught:
13 But the ones on the rock are those who, when they hear, receive the word with joy; and these have no root, who believe for a while and in time of temptation fall away. Luke 8:13
Believe is the condition for salvation.
Those who believe for a while are saved for a while.
It's up to you to prove, that those who are unbelieving, who no longer believe, still somehow satisfy the condition for salvation and eternal life, with scripture.
JLB